Indicating system



June 24, P H BETTS INDICATING SYSTEM Filed Jan. 31, 1927 HG. Z

Patented June v24, 1930 UNITED i STATES PHILANDEB n. nE'r'rs, 0E EEEMAB., NEW JERSEY, AssIGNon. To BELL TELEPHONE PATENT OFFICE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION NEW YORK ' INDICATING SYSTEM Application led January 3.1, 1927. Serial No. 164,952.

This invention relates Ito indicating .systems, and especially to systems for indicating the condition of electric space discharge tubes in a radio receiver or other apparatus l including such tubes.

ments and filament heating source, operaoutput electrode connected to the input elec' tiveness ofthe filaments being indicated by the green lamp being lighted and the other dark; an inoperative condition of the filaments by the red lam being lighted and the reen dark; 'and a ailure ofthe source, by t e absence of light from both lamps. The space current is sometimes derived from the same source as the filamentheating current, in which case the absence of light from both lamps likewise indicates the failure of the space current voltage supply.

Fig. 1 s a schematic showin of a radio receiver circuit -embodying a orm of the invention; and Fi .`2 is a schematic showing of a circuit embo ying another form of the invention.

In Fig. 1. an inductance coil 1 in an o en antenna 2 is variably coupled to an in uc-` tance coil 3 inthe input circuit of an electric space dischargetube 4,' the A. C. output circiut of which feeds the input circuit of a similar tube 5, which in turn has its trodes of a similar tube 6, which feeds a similar tube 7 By way o f exam le, tube 4 ma be a radio frequency ampli er, tube 5 a detector, -tube 6 an audio frequency am-4 plifying stage, and tube 7 a second audio frequenc am lif in sta e the late circuit of which ina yinelude ignthe ddlzted portion a loud spealn other receivi'n A source ofg force 10 supplies plate current and filament current for all of the tubes. `The filaments are connected in series with each other and with a green signal lamp V11l and with'a resistance 12, across source 10. The plates of the tubes are connected to the positive pole of the source 10, the plate voltages applied device (not shown) 'ng telephone receiver er1 unidirectional electromotive to tubes 4,5 and 6 being adjusted by a resistance 13 included in the plate circuit of those tubes, and an additional resistance 14 being included, in serial relation to resist-` ance 13, in the plate circuit of detector tube 5, to assist in adjusting the plate voltage applied to that tube. ,A red signal lamp 15 is connected across the path comprising lamp l1 and the tube filaments.

The lamp 11 may be a low voltage lamp, and the lamp 15 a high voltage lamp, the -impedance of the path comprising lampV 11 and the tube filaments, in parallel with lamp 15, being sufiiciently low, in comparison to resistance 12, to normally cause lamp 15 to be dark, or prevent lamp 15 from glowing brightl Preferably the filament of lamp 15 is o some material, as for example tungsten, which has a -temperature coefficient of resistance such that the filament has a pronounced tendency to darken when the voltage applied to the filament is decreased considerably below the normal filament voltage.

Normally the lampll is maintained bright by the current Howing from battery 10 and resistance 12 through its filament to the tube filaments. In this condition the lamp indicates positively that the tube filaments are intact and that the plate voltage is applied to the plate Acurrent circuit for the tubes. If thesource of plate and filament voltage fails, lamp 11 will cease t0 glow.

If, with the source of filament and plate voltage operative, a tube filament .burns out or breaks, the load on the source 10, due to the plate currents of the tubes and the filament current ofthe tubes, is removed, and the impedance of the circuit consisting ofthe tube filaments and lamp 11 at the lamp 15 becomes infinite. Y source 10 then divides between resistance 12 and lamp 15 in proportion to their impedances, and lamp 15 receives suficient current to cause it to become bright to thereby lindicate positively that the yplate current The voltage of to give the same indications as to thecondition of a plate current circuit and a tube.

filament heating circuit as are given by the lamp 11 and the lamp 15 in Fig. 1.` The lamp 1,1', as Well as the lamp 15', is a high voltage lamp, as foi' example a 10 watt, 11() volt tungsten filament lamp. It is in series with resistance 111. The path consisting -of lamp 11 and resistance 111 in series is connected in shunt to a resistance 12 which is in serial relation'to the tube filaments as in the case of resistance 12 of Fig. 1. The path which includes lamp 15 is connected in parallel relation to the tube filaments and includes a resistance 115' in series with the lamp. Tube 4 may be a radio frequency am lifier, tube 5 a detector, tube 6 an audio re:I quency amplifying stage, and tube 7 a second audio frequency amplifyingstage, the tube 7 operating a loud speaking telephone receiver, not shown. A resistance 20 is included in the path through the tube filaments, and the voltage drop due to the flow of the tube filament heating current through Y the resistance is utilized in fixing the stea are lighted may be 165 volts.

potential'of the grid of tube 7 in a manner Well known in the art but not shown in the drawing. 4

In Fig. 2`the source of voltage for supplying the filament heating current and the plate circuit current for the tubes is a motor generator 10', instead of the battery 10 shown in Fig. 1. The motor generator receives power from a line A21. A field rheostat 22 is provided for adjusting the voltage delivered by the motor generator, and a filter 23 prevents rapid fluctuations in this voltage from causing corresponding fluctuations in the tube filament heating cur.. rent and the unidirectional space current in the tubes.

Current for heating the filaments passes from filter 23 throughv two parallel paths, one consistin of resistance 12 and the other consisting o lamp 11 and resistance 111 in series, then through the filament of tube 7, resistance 20, and the filaments of tubes 6, 4 and 5, back to filter 23.

By way of example, the following conditions may obtain inv the system of Fig.y2.

The nor-malvoltage delivered at the output terminals of filter 23 when the tube filaments The normal filament-current may be 250 milliamperes, the tubes 4, 5 and 6 being Western f Electric type 215A tubes each having a fila ment voltage drop of about 1 volt, andthe tube 7 being a Western Electric type 221D tube having a filament voltage drop of about 5 volts. Each of the lamps 11 and 15 may be a' 110 volt, 10 watt tungsten filament lamp. The resistances 12, 111', 115', and 20 may have-values of 850 ohms, 40() ohms, 700 ohms, and 22 ohms, respectively.

meaeee What is claimed is:

1. An electric space discharge tube. having a filamentary cathode and an anode, a circuit including said cathode, a source of electromotive force for said circuit, connections from said source for supl ing space current to said tube, an impe ance connected in serial relation to said circuit with respect to said source, a circuit connected in shunt to said first circuit at the terminal of said impedance remote from said source, a lamp included in said second circuit, normall dark but lighting in response to voltage rom said source applied to said second circuit when saidfirst circuit is interrupted, a circuit connected in' shunt to said impedance, and a-signal'lam included in the latter circuit, normally llghted in response to voltage applied to the latter circuit from said impedance, due to crrent flowing from said source. through said impedance and said first circuit.

2. A radio receiver comprising a plurality of electric space discharge tubes having anodes and filamentary cathodes, a source of electromotive force, a filament heating circuit including said cathodes in serial relation to each other, an impedance connected in serialrelation to said circuit with respect to said source, connections from the terminal of said impedance adjacent said source to the anodes of said tubes for supplyin space current thereto, a circuit connecte in shunt to said first circuit at the terminal of said impedance remote from said source, a lamp included in said second circuit, normally dark but lightingy in response to voltage from said source applied to said second circuit when said first circuit is interrupted, a circuit connected in shunt to said impedance, and a signalv lamp included in the latter circuit, normally lighted in response to voltage ap lied to the latter circuit from said lmpe ance due to current flowing from said source through said inlpedance and said first circuit.

3, In combination, an electric discharge devlce having a thermionic cathode and an anode, a circuit including said cathode, an electrical source for supplying heating current to said cathode, an impedance element connected to said source in series with said circuit, a second circuit includin signal means connected in shunt to the rst circuit at the terminal of said impedance element remote from said source to give a pos- 1t1ve lndication of an inoperative condition of said first circuit, and a third circuit includln other signalin means connected effective y in series wit said first circuit to.

give a positive indication of an operative condition of said circuit..

4. In combination, an electric space dissource for supplying current to said circuit for heating said' cathode, an impedance element connected in series relation with said circuit with respect to said source, a circuit including indicatingmeans connected in shunt to said first circuit at the terminal of said impedance remote from said source to give a positive indication in response to current from said source when the first circuit is interrupted, and a circuit including a second indicating means connected in shunt to said impedance to give a positive indication in response to a voltage applied thereto due to current owing from said source through said im edance and the first circuit.

In witness whereof, I hereunto subscribe my name this 28th day of January A, D.,

PHILANDER. H. BETTS. 

